The Origins of Fiber Optic Communications

1
The Origins of Fiber Optic Communications

• Ch 1
• Fiber Optics Technicians Manual, 3rd. Ed
• Jim Hayes

2
Early Optical Communications

• The French used semaphores to transmit messages
  in the 1790s
• Later systems also sent optical signals through
  the air
• But clouds, rain, and other atmospheric
  disturbances can disrupt optical signals sent
  through the air
• Electric signals through wires avoid that problem
• Image from Wikipedia Semaphores

3
Guiding Light With Water

• Light in a stream of water stays inside the water
  and bends with it
• This was first demonstrated in the 1840s
• Image from glenbrook.k12.il.us/gbssci

4
Refraction (Bending) of Light

• Ray A comes from straight up and does not bend
  much
• Ray B comes at a shallow angle and bends a lot
  more
• Image from seafriends.org.nz

5
The View From Underwater

• Underwater, the light always shines down steeply,
  even when the Sun is low in the sky
• The whole sky appears in a limited round area
  called Snells Window
• Image from seafriends.org.nz

6
Light Coming Out of Water

• Animation on link Ch 1b
• http//www.phy.ntnu.edu.tw/ntnujava/viewtopic.php?
  t66

7
Total Internal Reflection

• There is a critical angle at which no light can
  be refracted at all, so 100 of the light is
  reflected
• Light is trapped in the water and cannot escape
  into the air
• This works with any dense medium, such as plastic
  or glass, the same way it works with water
• Image from glenbrook.k12.il.us

8
How Light Travels in Fiber

• Image from ece.umd.edu/davis

9
Bare Fiber

• During 1920-1950, thin, flexible rods of glass or
  plastic were used to guide light
• Such bare fibers require air outside each fiber
• Image from Wikipedia

10
Fiber With Cladding

• Developed in 1954 by van Heel, Hopkins Kapany
• Cladding is a glass or plastic cover around the
  core
• Protects the total-reflection surface
  contamination
• Reduces cross-talk from fibers in bundles

11
Medical Imaging

• By 1960, glass-clad fibers were available for
  medical instruments, to look inside the body
• The glass was unable to transmit light far enough
  for communications, because of impurities
• Attenuation (loss of light) was 1 decibel per
  meter

12
Decibels

• Decibels are a logarithmic scale of power
• Abbreviated dB
• A loss of 10 decibels means only 10 of the light
  gets through
• A loss of 20 dB means 1 of the light gets
  through
• Sunglasses stop 99 of light, so they cause a
  loss of 20 dB
• For communications, loss must be no more than 10
  or 20 decibels per kilometer

13
Optical Fiber in 1966

• Charles Kao developed a fiber that could transmit
  1 GHz (One billion bits per second)
• But attenuation was 1000 dB/km, so it could not
  transmit light far enough for practical
  communications

14
Corning

• Corning scientists developed low-attenuation
  silica glass fibers in 1970
• Corning Video At The Speed of Light
• Link Ch 1c on my Web page (samsclass.info)

15
Singlemode and Multimode Fiber

• Singlemode fiber has a core diameter of 8 to 9
  microns
• Multimode fiber has a core diameter of 50 or 62.5
  microns
• Both have a cladding diameter of 125 microns

16
Optical Fiber in 1977

• Telephone signals used infrared light with a
  wavelength of 850 nm to send data at 6.2 Mbps and
  45 Mbps
• Loss was 2 dB per km
• Repeaters were required every few kilometers
• The repeaters were electro-optical converting
  the light to electricity and then back to light

17
TAT-8

• In 1988 ATT laid the first fiber-optic
  transatlantic telephony cable
• 3,148 miles long
• Connected North America to France
• Repeaters every 40 miles
• 565 Mbps bandwidth
• Used 1300 nm light
• Attenuation 0.4 dB/km
• Image from att.com
• Info from link Ch 1e
• www.greatachievements.org/?id3706

18
Fiber Amplifier

• Special fiber with Erbium atoms in it is used to
  amplify light without changing it to an
  electrical signal first
• Uses stimulated emission, the same principle that
  makes lasers work
• Image from rp-photonics.com (Link Ch 1g)

19
Wavelength Division Multiplexing (WDM)

• Several signals can be sent through the same
  fiber simultaneously by using different
  wavelengths (colors) of light
• That means more bandwidthmore data per second

20
Freeway Analogy

• TAT-8 in 1980
• 565 Mbps
• Electro-optical repeaters
• TAT-12/13 in 1996
• 2.5 Gbps
• Optical amplifiers
• 1998
• 20 Gbps
• WDM with 8 wavelengths
• Image from www2.rad.com (Link Ch 1j)

21
Dense Wavelength Division Multiplexing (DWDM)

• Uses up to 100 wavelengths through a single fiber
• Bandwidth up to 1 Tbps (1000 Gbps)

22
Lennie Lightwave's Guide To Fiber Optics

• Basics
• From jimhayes.com/lennielw

23
Fiber Optics History

• Fiber optics began about 30 years ago in the RD
  labs (Corning, Bell Labs, ITT UK, etc.)
• First installed in Chicago in 1976
• By the early 1980s, fiber networks connected the
  major cities on each coast.

24
The 1980s

• By the mid-80s, fiber was replacing all the telco
  copper, microwave and satellite links
• In the 90s, CATV started using fiber to enhance
  the reliability of their networks
• CATV companies also discovered they could offer
  phone and Internet service on that same fiber and
  greatly enlarged their markets

25
Computers and LANs

• Started using fiber about the same time as the
  telcos
• Industrial links were among the first as the
  noise immunity of fiber and its distance
  capability make it ideal for the factory floor
• Mainframe storage networks came next, the
  predecessors of today's fiber SANs (storage area
  networks.)

26
Other Applications

• Aircraft, ship and automobile data buses
• CCTV for security
• Links for consumer digital stereo
• Today fiber optics is either the dominant medium
  or a logical choice for every communication
  system

27
Which Fiber Optics?

• "Outside Plant" fiber optics are used in
  telephone networks or CATV
• "Premises" fiber optics are usedin buildings and
  campuses
• Just like "wire" which can mean lots of different
  things - power, security, HVAC, CCTV, LAN or
  telephone - fiber optics is not all the same.

28
Installing Fiber Optics

• Fiber is harder to install than 100 Mbps copper
  Ethernet cable
• But fiber is MUCH faster, so the infrastructure
  wont need to be upgraded so soon
• And gigabit Ethernet is harder to install
• LAN copper cable is delicate. It only has a 25
  pound pulling tension limit and kinks will ruin
  the high speed performance
• Fiber has more strength and greater tolerance to
  abuse than copper wire

29
Safety First!

• The light in the fiber can burn your retina
• NEVER look into a fiber unless you know no light
  is present - use a power meter to check it
• The infrared light is invisible

30
Fiber Shards

• When you cleave fiber, there are small scraps of
  glass produced.
• These scraps are very dangerous!
• The cleaved ends are extremely sharp and can
  easily penetrate your skin
• They are even worse in your eyes, mouth, etc.

31
Safety Rules

• Wear glasses or safety glasses
• Dispose of all scraps properly
• Put scraps on black tape
• Use a properly marked trashcan
• Work on a black pad which makes the slivers of
  glass easier to spot
• Do not drop scraps on the floor
• Do not eat or drink anywhere near the work area

32
Chemical Safety

• Fiber optic splicing and termination use various
  chemical adhesives and cleaners
• Follow the instructions for use carefully
• Isopropyl alcohol, used as a cleaner, is flammable

33
Zero Tolerance for Dirt

• Airborne particles are about the size of the core
  of Single Mode fiber
• They absorb lots of light and may scratch
  connectors if not removed
• Dirt on connectors is the biggest cause of
  scratches on polished connectors and high loss
  measurements

34
Hygiene Rules

• Work in a clean area avoid dust
• Keep dust caps on all connectors
• Use lint free pads and isopropyl alcohol to clean
  connectors